Automatic elevator control



Nov. 17, 1959 M. N. NYBERG AUTOMATIC ELEVATOR CONTROL 2 `Sheets-Shlee'c2 Filed Feb. 26, 19,58

United States Patent O 2,913,070 g AUTOMATIC ELEVATOR CONTROL Magnus N.Nyberg, Oceanside, N.Y., assignor to Hydraulic Elevator & Machine Co.,Inc., Brooklyn, N.Y., a corporation of New York Application February 26,1958, Serial No. 717,688

15 Claims. (Cl. 187-29) This invention relates to hydraulic elevatorsystems and more particularly to the control of such systems.

Many existing hydraulic elevator systems are mechanically controlled bymeans of cables and pulleys which activate the valving mechanismsassociated with the hydraulic ram that drives the elevator cab. Thecables must be manipulated by a skilled operator. In addition, suchcontrols, besides being cumbersome, are slow operating.

It is, accordingly, a general object of the invention to provideimproved controls for hydraulic elevator systems.

It is another general object of the invention to provide electricalcontrols for hydraulic elevator systems.

It is amore specific object of the invention to replace the mechanicalcontrols, such as the cables and pulleys of a hydraulic elevator system,with electrical controls which are both fast operating and compact.

It is another specific obiect of the invention to replace the mechanicalcontrols which require a skilled operator by electrical controls whichmay be operated by unskilled persons.

Still another specic object is to provide hydraulic control means inconjunction with a hydraulic elevator system whereby such system isconditioned for automatic control by a modern electrical control system.

Other objects and various other features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specication in conjunction with the accompanyingdrawings. In said drawings, which show for illustrative purposes only,preferred forms of the invention:

Fig. 1 schematically shows a hydraulic-elevator system incorporatingcontrol means in accordance with the invention;

Fig. 2 shows, in accordance with one embodiment of the invention,electrical-signal-operated valve means and hydraulic-control means, asemployed in the organization of Fig. l, the valve means being inlongitudinal section;

Fig. 3 shows electrical control means, as used in the combination ofFig. 1;

Fig. 4 is a diagram similar to Fig. 2 and showing another embodiment ofthe electrical-signal operated valve means and hydraulic-control meansof Fig. l.

Briefly, the invention contemplates electrical control apparatus for ahydraulic elevator system, as of the type wherein the elevator cab isdriven to different levels by a hydraulic ram. The apparatus forcontrolling the operation of the hydraulic ram comprises a plurality ofoor selectors for generating electric control functions indicating theselected oors. Level indicating means are included for generating otherelectric control functions indicating the actual level of the elevatorcab. A control means which is responsive to both the floor selectors andthe level indicating means generates electrical control signals relatedto the relationship between the oor selected and the level indicated. Anelectrical signal operated valving means is responsive to the controlmeans the actual level of the elevator cab 10.

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to control a hydraulic control means which regulates the movement of thehydraulic ram.

Referring to Fig. 1, a hydraulic elevator system is shown wherein anelevator cab 10 is positioned up and down a shaft by a hydraulic ram 12.As the elevator cab 10 moves from door to oor, a synchro generator 14which is coupled to the counterweight-pulley shaft 16 feeds back to asynchro motor 18 signals indicating the instantaneous elevation of theelevator cab. When an operator Wishes to move the elevator to adifferent floor, he depresses the push button associated with that ooron the floor selector panel 20, which generates a signal characteristicof the selected floor.

At the same time, the synchro motor 18 in response to the synchrogenerator 14 transmits a signal indicating These two signals arecompared in the electrical control means 22 and if the selected floor isbelow the present position of the elevator cab, the down valve means 24is energized, causing the hydraulic control means 28 to bleed iluid fromthe hydraulic ram 12. When the elevator cab reaches the selected floor,the electrical control means 22 de-energizes the down valve means 24 andthe hydraulic ram stops.

If, on the other hand, the selected oor is above the actual level of theelevator cab, the electrical control means 22, in a similar manner,energizes the up valve means 26. The hydraulic control means 28 feedsiluid to the hydraulic ram 12, and the elevator cab starts on an upwardmotion. This upward motion continues until the selected iloor and theindicated iloor are the same. At this time, the up valve means 26 isde-energized and the hydraulic ram stops.

Fig. 2 shows the down valve means 24, which includes the normally closedsolenoid operated valve 24a and the normally open solenoid operatedvalve 2411; the up valve means 26, which includes the normally closedsolenoid operated valve 26a and the normally open solenoid operatedvalve 26h; and the hydraulic control means 28, which includes themainvalve 30 and the pilot valve 32. During the rest period, all valvesolenoids are de-energized, and the main valve 30 and pilot valve 32 arein the neutral positions shown.

When the elevator cab is to move downward, a signal on the line 25 opensthe solenoid operated valve 24a and closes the solenoid operated valve24b. The fluid sink is coupled via the valve 24a and the pipes 37, 34and 35 to the fluid chamber 36. Since the area of the piston 38 isgreater than the area of the cup 39, the Valve stem 40 is driven upward.The valve element 62 is correspondingly displaced, and fluid from thehydraulic ram 12 enters the port 64 and leaves via the port 66 to theuid sink, thus allowing the elevator cab to descend.

At the same time, the stem 48 of the pilot valve 32 is moved downwardbecause of the mechanical linkage 50, and a connection is establishedbetween the pilotvalve ports 52 and 56. Since the normally open solenoidoperated valve 24b is now closed, this connection at present has noeffect on the valve system. When the elevator cab reaches the desiredoor, the signal on the line 25 terminates, causing the closure of thesolenoid operated valve 24a and the opening of the solenoid 0peratedvalve 24b. lFluid from the fluid source passes through the now-opensolenoid operated valve 24b, the pipe 68, through the ports 56 and 52,and the pipes 57 and 35 to the fluid chamber 36. The main-valve stem 4t)starts falling and the valve stern 48 rises. This action continues untilthe connection between the ports 52 and 56 is closed. At this time, themain and pilot valves have returned to their rest positions, and thehydraulic ram 12 stops.

. When the elevator -cab is to be moved upward, a signal on the line 27energizes the normally closed solenoid operated valve 26a and thenormally open solenoid operated valve 26b.v Fluid is fed to the iuidchamber 36 from the uid source via the now-opened ysolenoid operatedvalve 26a and the pipes 33-35. The main-valve stem 40 moves downward,drawing the valve element 62 with it. The port 64 connected to thehydraulic ram 12 is coupled to the fluid source via the port 44. Fluidenters the hydraulic ram l2 and the elevator cab ascends. At the sametime, there is an upward movement of the stem 48 in the pilot valve 32,resulting in a connection between the ports 52 and 54; since at present,the solenoid operated valve 26h is closed, the existence of a connectionbetween ports 52 and 54 has no immediate eiect on the valve system.However, when the desired oor is reached, the signal on the line 27terminates, and the solenoid operated valves 26(a-b) are de-energized.Fluid from the iiuid chamber 36 passes Via the pipes 35 and 57, theports S2 and 54, and the pipes 58 through the now-- opened solenoidoperated valve 26b to the fluid sink.

The main-valve stem 40 is driven upward with accompanying downwardmovement of the pilot-valve stem 48, which continues until theconnection between the ports 52 and 54 is closed. At this time, thehydraulic ram stops, since there is no longer any connection between theports 44 and 64 of the main valve 30.

The electrical control means 22, which controls the down valve means 24and the up valve means 26 in response to signals from the Hoor selectorpanel and the synchro generator 14, is shown in Fig. 3. Associated witheach oor is a cam-operated switch 80, a level relay 82, and a drivecontrol relay 84. These elements, cooperating with the floor selectorpanel 20, energize valve controls 86 which are used to actuate the upand down valve means.

To insure precise floor-leveling, a level sensor 90 actuates levelers88, which act as tine operators on the valve controls 86 when theelevator cab approaches the desired iloor. In particular, the levelsensor 90 includes a pair of iron-core inductors 92a and 92b carried bythe elevator cab and positioned about four feet apart along a verticalline on the outside of the cab. Centered about the center level of eachfloor and secured to the building or elevator shaft is a ferromagneticstrip 92e. This strip is vertically disposed and in close adjacency tothe ironcore inductors 92(a-b). The cooperation of these elements inleveling the elevator cab will be hereinafter described in conjunctionwith the overall operation of the control means 22. l

As an example of the electrical-control means 22 controlling an upmotion, an operator pushes the button 20-3 to move the elevator cab tothe third floor, it being assumed that the elevator cab is at the secondfloor (the condition shown in Fig. 3). The depression of the buttonZtl-3 energizes the relay 84-3 by completing a path through the normallyclosed contacts 82-3-b and 84-3b; holding contacts 84-3a, receivingcurrent via the contacts 82-3a, keep the relay 84-3 in this energizedcondition after the release of the push button. The energization of therelay 84-3 closes a circuit from the line 23 through the now closedcontacts 84-3c, through the normally closed contacts 82-4c, to the line94 to energize the up relay 87.

When the up relay 87 is energized, a signal is fed via the line 27 tothe up valve means 26, and the hydraulic ram 12 drives the elevator cabupward. At the same time, the normally closed contacts 87-b are openedto prevent any possible energization of the relay 85 which controlsdownward elevator-cab motion. As the elevator cab moves, the synchromotor 18 receives signals from the synchro generator 14 to drive thecam-operated switches 80. When the floor of the elevator cab is withinapproximately a foot and a half of the third floor, the cam operatedswitch 80-3 closes, causing the energization of relay 82-357and thenormally closed sets of contacts v is cut off when inductor 92h movespast the lower end of,

energize the relay 82-1.

of this relay open. When the contacts 82-3a open, the holding circuit(S4-3a) for the relay 84-3 is broken, and the relay drops out. Droppingout relay 84-3 terminates current flow to the relay 87 via the line 94.

However, just prior to the operation of the cam-operated switch Sil-3,the level sensor 90 starts operating; in particular, the iron-coreinductor 92a comes in operative proximity with the third-floorferromagnetic strip 92c-3, and the impedance of this element is greatlyincreased. The increase in impedance causes the dropping out of relay96, whose coil is connected in series with the ironcore inductor 92a.Dropping out the relay 96 causes its normally closed contacts 96a tocouple power to the relay 37. Thus, when the cam-operated switch -3closes, to fle-energize, in particular, the relay 84-3, the up levelerrelay 96 assumes the role of supplying current to the up relay 87, andthe elevator cab continues to move upward. This upward movement proceedsuntil the iron-core inductor 92a moves just past the top end of theferromagnetic strip 926-3. At this time, the impedance of the iron-coreinductor 92a decreases, and the up leveler relay 96 is again energized.Its normally closed contacts 96a open, and all power is removedfrom theup relay 87. The elevator cab thus stops at the third floor.

If, for any reason, there is an overshoot in the leveling operation, theiron-core inductor 9217 becomes operatively close to the ferromagneticstrip 92c-3 and its impedance rises. The increase in impedance causesthe down leveler relay 98 to drop out, and current is fed to the downrelay S5 which then supplies power via the line 25 to the down valvemeans 24 to start a downward movement of the elevator cab. Down controlthe ferromagnetic strip 92c-3, at which time the cab is leveled at thethird oor.

As an example of downward motion control, it will again be assumed thatthe elevator cab is at the second floor (the condition illustrated inFig. 3) and that the operator wishes to go to the rst floor. In thiscase, the operator momentarily depresses the push button 20-1, whichpasses a current through` the normally closed contacts 82-1b to thenormally closed contacts 84-1b, energizing the relay 84-1. With therelay 84-1 energized, its holding contacts 84-1a receive current via thenormally closed contacts 82-1a of the level relay 824, so that relay84-1 remains energized. The energization of the drive control relay 84-1establishes a current path from the line 23, via the now-closed contacts84-1c, the normally closed contacts 82-1c, and the line 99 to the downrelay 85. rent is fed via the line 25 to the down valve means 24,

-thus starting downward elevator cab motion. At the same time, thenormally closed contacts h are opened and the up relay 85 is disabled toprovide an interlock; up relay 87 cannot be energized while the downrelay 85 is energized.

The elevator cab starts moving down. When it is approximately two feetfrom the desired level of the rst ioor, the iron-core inductor 92];becomes operatively disposed opposite the rst-oor ferromagnetic strip92c-1. The impedance of the solenoid 9212 greatly increases, causing thede-energization of the relay 98, whose coil is in series with thesolenoid of dow-n leveler relay 98. Re-` lay 98 drops out, and itsnormally closed contacts 98a establish a current path yfrom the line 23to the solenoid of down relay 85. Thus, the down relay 85, at this time,is being energized via two paths. However, when the oor of the elevatorcab is about 18 inches from the desired level, the cam-operated switchilis closed to ent'upon the level sensor 90 and when the oorof'the ele#Down relay 85 becomes energized, and a cur-V The energization of thisrelayv vatorcab reaches the level of the first floor, the iron-coreinductor 92b is just leaving the bottom edge of the vfirstoorferromagnetic strip 92c-1, and the leveler relay 98 becomesre-energized. Re-energization of relay 98 causes its normally closedcontacts 98a to open, and all power t0 the down relay 85 ceases. Theelevator cab thus stops at the desired level of the irst iioor.

Although the electrical control means is shown for servicing afour-floor system, it should be realized that any number of floors canconveniently be serviced by the addition of the required number of pushbuttons 20 and the associated Hoor-level elements, which include acam-operated switch 80, a level relay S2, a drive relay 84, and aferromagnetic strip 92C.

Fig. 4 shows an alternative embodiment of the "down Valve means 24, theup valve means 26 andthe hydraulic control means 28 for operation with ahydraulic cam having a head and tail section. Since there are manysimilarities between this and the embodiment of Fig. 2 primed referencecharacters will be employed for corresponding elements.

When the elevator cab is to be moved downward, a signal on the line 2Senergizes the normally closed solenoid-operated valve 24a and thenormally open solenoid operated valve 24b'. Fluid is bled from the fluidchamber 36 of the main valve 30' and pressure from the fluid sourceoperating through port 44 against cup 39' forces the main-valve stem 40'to the left. The valving element 62' follows this motion until there isa connection between the ports 64 and 66', which permits the flow ofiluid from head of the hydraulic ram 12 to the fluid sink. There is alsoa connection established between the tail of the hydraulic ram 12 andthe liuid sink via the ports 46' and 66'. Fluid is drained from both thehead and tail sections of the hydraulic ram. At the same time, there isa rightward movement of the stem 48' in the pilot valve 32', resultingin a connection of the port 52' with the port 54. Since the solenoidvalve 24b' is at this time closed, this movement has no effect on thevalve system;

Athence via the pipe 76 through the ports 54' and 52', the

normally opened solenoid-operated valve 26h' and the pipe 70, andcontinues until the main and pilot valves reach their rest positions.

When the elevator cab is to be moved upward, a signal on line 27energizes the solenoid-operated valves 26a' and 26b'. Fluid enters thefluid chamber 38' from the uid source via the now-openedsolenoid-operated valve 26a', and the pipe 70. The main-valve stem 40moves to the right, and when the valve eiement 42 is completelydisplaced, there is a connection between the ports 44' and 46', directlysupplying'the tail of the hydraulic ram 12 from the uid source. Theconcurrent movement of the valve element 62 establishes a connectionbetween the ports 64' and 66 to permit a discharge of fluid from thehead of the hydraulic ram. At the same time, the stern 48' of thepilot-valve 32' is moved to the left, permitting a connection of theports 52' and 56'. Since the solenoidoperated valve 2Gb is closed atthis time, this connection does not affect the valve system.

When the elevator cab reaches the desired floor, the signal on the line27 terminates, and the solenoid-operated valves 26a' and 2Gb' arede-energized. Fluid leaves the fluid chamber 36" via the pipe 70, thenow-opened solenoid-operated valve 26b', the pipe 75, the ports 52' and56' and drains to the iiuid sink. Fluid in the uid chamber 36' continuesto bleed ofI until the connection between the ports 52' and 56' isbroken.

There have thus been shown two embodiments of electrifying the hydrauliccontrols for a hydraulic operated elevator system. The system, as shown,requires very little mechanical skill to operate and is highly reliableand fast operating. In particular, it will be seen that the invention isapplicable to existing hydraulic elevator systems with minimummodiiication, so that such existing systems may be fully modernized withmodern electric-control systems, including those of the mostsophisticated nature, the presently described electrical controls beingmerely illustrative.

While the invention has been described in detail, for the preferredforms shown, it will be understood that modifications may be madewithout departing from the scope of the invention as defined in theclaims which follow.

What is claimed is:

1. In a hydraulic elevator system wherein the elevator cab is driven todifferent oors by a hydraulic ram, apparatus for controlling theoperation of the hydraulic ram comprising a plurality of floor selectorsfor generating electrical control functions indicating the selectedoors, indicating means for generating electrical control functionsindicating the level of the elevator cab, a control means responsive tosaid door selectors and said level indicating means, said control meansgenerating a first electrical signal when the selected oor is above theindicated level and a second electrical signal when the selected Hoor isbelow the indicated level, a down valve means energizable by the firstelectrical signals, an up valve means energizable by the secondelectrical signals, a hydraulic control means responsive to said upvalve means and said down valve means for controlling the hydraulic ramin driving the elevator cab, and means responsive to dse-energizing saidup and down valve means for stopping said cab.

2. In a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling thequantity of liquid in the hydraulic ram comprising a plurality of levelselectors for generating electrical signals indicating selected levels,level-indicating means for generating an electrical signal indicative ofthe instantaneous cab level, a control means responsive to saidlevel-indicating means and to said level selectors for generatingelectrical signals, electrical signal operated valving means operated bysaid control means, a source of pressure iiuid, a sink for receivingfluid, and a pressure operated valving means selectively coupling anddecoupling the hydraulic ram with respect to said source and withrespect to said sink, said signal operated valving means controlling thepressure exerted on said pressure operated valving means, the sense ofconnection from said control means to said electrical signal operatedvalving means being such that upon de-energizing said signal-operatedvalving means, said ram is decoupled from said source and from saidsink.

3. The apparatus of claim 2 wherein a change in pressure on saidpressure operated valving means in a first direction couples thehydraulic ram to said sink and a change in pressure in a seconddirection couples the hydraulic ram to said source.

4. The apparatus of claim 2 wherein said pressure operated valving meansincludes a luid chamber and valve elements responsive to said fluidchamber for coupling the hydraulic ram to said source or said sink, andsaid signal operated valving means selectively coupling said source andsaid sink to said pressure chamber.

5. The apparatus of claim 4 wherein said signal operated valving meansincludes a iirst valve for coupling said source to said fluid chamberand a second valve for coupling said sink to said fluid chamber.

6. The apparatus of claim 5 wherein said first valve is activated whenthe selected level is lower than the indicated level and said secondvalve is activated when the selected level is higher than the indicatedlevel.

7. In a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling thequantity of fluid in the hydraulic ram comprising a plurality of iioorselectors for generatingelectrical control function'sindicating selectedfloors, level indicating means for generating control functionsindicating the level of the elevator cab, an electrical control meansresponsive to said fioor selectors and said level indicating means, saidelectrical control means generating a first control signal when theselected floor is above the indicated level and generating a secondelectrical signal when the selected floor is below the indicated level,a first electrically operated valve activated by the first controlsignal, a second electrically operated valve activated by the secondcontrol signal, a source of fiuid under pressure, said source beingcoupled to one of said electrically operated valves, a sink forreceiving fluid, said sink being coupled to the other of saidelectrically operated valves, and pressure sensitive hydraulic controlmeans including valve means having a first positional relationshipdetermining ascent of said cab, a second positional relationshipdetermining descent of said cab, and a third positional relationshipdetermining arrest of cab movement, and hydraulic means responsive tooperations of said rst and second electrically operated valves todetermine the first, second, and third positional relationships of saidvalve'means.

8. The apparatus of claim 7 wherein said pressure sensitive hydrauliccontrol means includes a fluid chamber coupled to said first and secondelectrically operated valves, a piston operatively disposed at one endof said uid chamber and a valve coupled to said piston, said valveselectively coupling the hydraulic ram to said source and said sink.

9. In a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling theoperation of the hydraulic ram comprising a plurality of floor selectorsfor selecting different elevator cab levels, level indicating means forindicating the level of the elevator cab, said floor selectors and saidlevel indicating means generating electrical control functions, anelectrical control means for receiving the electrical control functions,said electrical control means including first and second signalgenerators for generating a first electrical signal when the selectedfloor is higher than the inidcated level and generating a second controlsignal when the selected oor is lower than the indicated level, a sourceof fluid under pressure, a sink for .receiving fluid, first and secondsolenoid operated valves responsive to said first signal generator, saidfirst solenoid operated valve being coupled to said source, said secondsolenoid operated valve being coupled to said sink, third and fourthsolenoid operating valves responsive to said second signal generator,said third solenoid operated valve being coupled to said source, saidfourth solenoid operated valve being coupled to said sink, a mainhydraulic valve, said main hydraulic valve having a fluid chambercoupled to said first and said fourth solenoid operated valves, a mainpiston disposed at one end of said liuid chamber, a main valving meansfor selectively coupling the hydraulic ram to said source and said sink,a main mechanical member for linking said main piston to said mainvalving means, and a pilot valve responsive to said main mechanicalmember, said pilot valve being coupled to said second and thirdsolenoid-operated valves and said fluid chamber, said pilot valve havingpilot valving means responsive to said main mechanical member toselectively couple said fluid chamber to said second and third receivingsolenoid-operated valves, said yfirst and second solenoid-operatedvalves being activated when a signal from said first signal generator toincrease the fluid in said uid chamber, the increase in fluid causing adisplacement of said main valving means and said pilot valving meansform a rest position, said first and second solenoid operated valvesbeing deactivated when the indicated level is the same as the selectedfloor to permit said pilot valving means to couple said fluid chamber tosaid sink.

' 10. The apparaus of claim 9 wherein said third and fourth solenoidoperated valves are activated when a signal is generated by said secondsignal generator to de-- crease the fluid in said tiuid chamber, thedecrease in iluid causing an'opposite displacement of said main valvingmeans and said pilot valving means, said third and fourth solenoidoperated valves being deactivated when the indicated level is equal tothe selected oor to permit said pilot valving means to couple saidV uidchamber to said source.

11. In a hydraulic elevator system wherein the elevator cab is driven todiiierent levels by a hydraulic ram, apparatus for controlling thequantity of fluid in the hydraulic ram comprising a plurality of oorselectors for generating electrical control functions indicatingselected floors, level indicating means for generating control functionsindicating the level of the elevator cab, an electrical control meansresponsive to said floor selectors and said level indicating means,hydraulic control valve means for said ram, a hydraulic pressure sourceand a sink, solenoidoperated valve means for selectively connecting saidcontrol-valve means to said source and to said sink, said electricalcontrol means being operatively connected to said solenoid-operatedvalve means, said valve means establishing a locked-flow condition forhydraulic fluid fiowing into and out of said ram when saidsolenoidoperated valve means is de-energized.

12. In a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling thequantity of uid in the hydraulic ram comprising a plurality of oorselectors for generating electricalcontrol functions indicating selectedfloors, level indicating means for generating control functionsindicating the level of the elevator cab, an electrical control meansresponsive to said fioor selectors and said level indicating means,hydraulic control valve means for said ram, a hydraulic pressure sourceand a sink, solenoidoperated valve means for selectively connecting saidcontrol-valve means to said source and to said sink; said electricalcontrol means having a first condition determining excitation of saidsolenoid-operated valve means to establish a fluid flow from said sourceto said ram, a second condition determining excitation of saidsolenoidoperated valve means to establish a fluid flow from said ram tosaid sink, and a third condition determining a deenergized condition ofsaid solenoid-operated valve means; and means operative uponde-energizing said solenoidoperated valve means for stopping iiuid ow toand from said ram.

13. ln a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling thequantity of fluid in the hydraulic ram comprising a plurality of floorselectors for generating electrical control functions indicatingselected floors, level indicating means for generating control functionsindicating the level of the elevator cab, an electrical control meansresponsive to said ioor selectors and said level indicating means,hydraulic control valve means for said ram, a hydraulic pressure sourceand a sink, solenoidoperated valve means for selectively connecting saidcontrol-valve means to said source and to said sink; saidsolenoid-operated valve means havin-g a first energized conditiondetermining hydraulic connections of said control-valve means to drivesaid cab upwardly, said solenoid-operated valve means having a secondenergized condition determining hydraulic connections of saidcontrol-valve means to drive said cab downwardly, said solenoid-operatedvalve means having a third and de-energized condition determininghydraulic connections to said control-valve means to stop said cab; andelectrical control connections to said solenoid-operated valve meansfrom-v said electrical control means.

14. In a hydraulic elevator system wherein the elevator cab is driven todifferent levels by a hydraulic ram, apparatus for controlling thequantity of uid in the hydraulic ,ram comprising a plurality of floorselectors for generating electrical control functions indicatingselected floors, level indicating means for generating control functionsindicating the level of the elevator cab, an electrical control meansresponsive to said oor selectors and said level indicating means,hydraulic control valve means for said ram, a hydraulic pressure sourceand a sink, solenoid-operated valve means for selectively connectingsaid control-valve means to said source and to said sink; saidcontrol-valve means including a main valve having a movable valve memberfor which ow to and from said ram is stopped when said valve member isin a central position, said ram being connected to ascend when saidmember is positioned to one side of said central position and beingconnected to descend when said 15. The elevator system of claim 14,wherein said hydraulic means is eective to center said main-valve memberfor the de-energized condition of said solenoidoper.

ated valve means.

References Cited in the file of this patent UNITED STATES PATENTS DunnJuly 24, 1917 Furlow June 4, 1918

